Liquid crystal display device

ABSTRACT

A liquid crystal display device having a high definition screen in which a pixel electrode is formed in a region surrounded by a gate line and a drain line, and a trapezoidal protrusion having an upper surface and inclined surfaces is formed below the gate line. Since a TFT is formed over a trapezoidal protrusion and a channel portion is formed over the upper surface and the inclined surfaces of the trapezoidal protrusion, the width of the channel portion can be enlarged compared to that of a channel portion formed over a plane. The pixel electrode is in contact with a source electrode at the inclined surface of the trapezoidal protrusion. This configuration allows the TFT and a contact of the pixel electrode and a source electrode to be formed over part of the trapezoidal protrusion.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2010-243411 filed on Oct. 29, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and particularlyrelates to a liquid crystal display device capable of maintainingbrightness even when the screen is high definition and the size of apixel is decreased.

2. Description of the Related Art

A liquid crystal display device includes a TFT substrate, a counterelectrode opposing the TFT substrate, and liquid crystals put betweenthe TFT substrate and the counter substrate. The TFT substrate haspixels including electrodes, thin film transistors (TFT), etc. formedthereon in a matrix form. The counter electrode has color filters, etc.formed at positions corresponding to the pixel electrodes of the TFTsubstrate. The liquid crystal display device forms images by controllinglight transmittance of each pixel using liquid crystal molecules.

Since liquid crystal display devices are flat and light in weight, theyare applied in various fields. Small sized liquid crystal displaydevices are used generally for mobile phones, DSCs (digital stillcameras), etc. In the small-size liquid crystal display devices, thesize of the pixel is decreased in order to maintain the definition ofthe screen. Each of the pixels includes, in addition to the pixelelectrode, the TFT, a through hole formed for connecting the TFT and thepixel electrode, etc. It is difficult to decrease the size of the TFTand the through hole correspondingly with the decrease of pixel size.Therefore, when the size of the pixel is decreased, the area of thepixel electrode is reduced. The transmittance of a liquid crystaldisplay panel is thus lowered and the brightness of the liquid crystaldisplay device is decreased.

In addition, viewing angle characteristics issue a problem in the liquidcrystal display device. The viewing angle characteristics are aphenomenon that brightness and chromaticity differ from when the screenis observed from the front to when viewed from an oblique direction. AnIPS (In Plane Switching) system, a system which operates liquid crystalmolecules by a horizontal electrode field, has good characteristics inrespect of the viewing angle characteristics.

Since, in the IPS system, the pixel electrode and the counter electrodeare formed on the TFT substrate side, the problem of the transmittanceis further severe. Various kinds of IPS systems exist; for example, asystem predominant at current forms a counter electrode as a solidplane, disposes a comb-shaped pixel electrode thereover with aninsulating film being put between the two, and generates an electricfield between the two electrodes to rotate liquid crystal molecules.This system allows the transmittance to be increased. JP-A-2007-328210describes a liquid crystal display device using such a system.Incidentally, a system that forms a pixel electrode as a solid plane anddisposes a comb-shaped counter electrode thereover with an insulatingfilm being put between the two is similar to the system mentioned above.

On the other hand, JP-A-2009-168878 discloses a configuration such thatforms a counter electrode in a layer identical with the gate electrode,and forms a comb-shaped pixel electrode thereover with a gate insulatingfilm and a protective insulating film put between them. According toJP-A-2009-168878, this configuration enables the number of layers in theTFT substrate to be reduced.

SUMMARY OF THE INVENTION

Recently, a high definition screen such as VGA (video graphics array:640×480 dots) has been demanded also for a small-sized liquid crystaldisplay device. Since the dot comprises a set of three pixels, that is,a red pixel, a green pixel, and a blue pixel, the number of pixels are1920×480. In order to implement VGA in a 3 inch screen, the minordiameter of the pixel is required to be as small as 32 μm.

To maintain a predetermined transmittance even when the size of thepixel is decreased, it is necessary to dispose TFT, through hole, etc.in a small area, and increase the ratio of the pixel electrode area asmuch as possible. However, size-reduction of the TFT and the throughhole for connecting the source electrode and the pixel electrode of theTFT, in accordance with the reduction of the pixel area, is limitedregarding the performance of the liquid crystal display device and themargin of the manufacturing process. In the configuration according toJP-A-2009-168878, the through hole is formed in only one layer, that isthe inorganic passivation film, and the area of the through hole can bedecreased to thereby improve the transmittance. However, this is stillnot sufficient.

An object of the present invention is to provide a liquid crystaldisplay device capable of maintaining the brightness of the liquidcrystal display device by increasing the ratio of an area of a pixelelectrode in a pixel without lowering the performance of a TFT whileensuring the margin of the process even when the size of the pixel isdecreased. While an IPS system liquid crystal display device is used asan example for describing the problem in the conventional technology, aTN (twisted nematic) system and a VA (vertical alignment) system alsohave a substantially similar problem.

The configuration according to the present invention for achieving theobject is described below.

(1) A liquid crystal display device comprising:

a TFT substrate;

gate lines extending in a first direction and arranged in a seconddirection over the TFT substrate;

drain lines extending in the second direction and arranged in the firstdirection over the TFT substrate;

pixel electrodes each formed in a region surrounded by the gate linesand drain lines;

trapezoidal protrusions formed discretely in the first direction belowthe gate lines, each of the trapezoidal protrusions having an uppersurface and inclined surfaces in the cross section taken along a planeorthogonal to the first direction;

a gate insulating film formed over the gate lines;

a semiconductor layer formed on the gate insulating film;

drain electrodes formed by the drain lines over the semiconductor layer;

source electrodes formed over the semiconductor layer; and

channel portions defined by the space between the drain electrodes andthe source electrodes, each of the channel portions being formedcovering the upper surface and the inclined surfaces of the trapezoidalprotrusion;

wherein the pixel electrode and the source electrode are in contact witheach other on the inclined surface of the trapezoidal protrusion.

(2) When an inorganic passivation film is interposed between the sourceelectrode and the pixel electrode, a through hole is formed in theinorganic passivation film above the upper surface of the trapezoidalprotrusion. The source electrode and the pixel electrode areelectrically connected via the through hole.

(3) A continuous bank is formed below the gate line instead of thetrapezoidal intrusion formed discretely below the gate line. The TFT isformed over the bank, and the source electrode and the pixel electrodeare electrically connected over the inclined surface of the bank.

(4) When the continuous bank is formed below the gate line instead ofthe trapezoidal protrusion formed discretely below the gate line, theTFT is formed over the bank, and the inorganic passivation film isinterposed between a source electrode and a pixel electrode, a throughhole is formed in the inorganic passivation film above the upper surfaceof the bank. The source electrode and the pixel electrode areelectrically connected via the through hole.

(5) The configurations described above can be applied to any of the IPSsystem, the TN system, and the VA system.

According to the configuration (1), the TFT is formed at the trapezoidalprotrusion and a thorough hole is not used. Thus, most of the pixelregion can be used for the pixel electrode and the transmittance of theliquid crystal display panel can be improved.

According to the configuration (2), even when the source electrode andthe pixel electrode of the TFT are electrically connected via thethrough hole formed in the inorganic passivation film, the through holeis formed above the trapezoidal protrusion. Thus, most of the pixelregion can be used for the pixel electrode and the transmittance of theliquid crystal display panel can also be improved.

According to the configuration (3), the TFT is formed on the continuousbank and a through hole is not used. Thus, most of the pixel region canbe used for the pixel electrode and the transmittance of the liquidcrystal display panel can be improved.

According to the configuration (4), even when the source electrode andthe pixel electrode of the TFT are electrically connected via thethrough hole formed in the inorganic passivation film, the through holeis formed above the upper surface of the bank. Thus, most of the pixelregion can be used for the pixel electrode and the transmittance of theliquid crystal display panel can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a TFT substrate for Embodiment 1;

FIG. 2 is a cross sectional view of a liquid crystal display panelcorresponding to a cross section taken along the line A-A in Embodiment1;

FIG. 3 is a cross sectional view of a channel portion of a TFT;

FIG. 4 is a perspective view of a trapezoidal portion;

FIG. 5 is a perspective view of the trapezoidal portion with a gate lineformed thereover;

FIG. 6 is a perspective view of the trapezoidal portion with asemiconductor layer formed thereon;

FIG. 7 is a perspective view of the trapezoidal portion with a drainelectrode and a source electrode formed thereover;

FIG. 8 is a perspective view showing a state where a pixel electrode isformed in a pixel region and in an inclined surface of the trapezoidalportion;

FIG. 9 is a perspective view showing a relationship of the drainelectrode, the source electrode, the channel portion, and the pixelelectrode in Embodiment 1;

FIG. 10 is a plan view of a TFT portion formed over the trapezoidalportion;

FIG. 11 is a cross sectional view taken along the line B-B in FIG. 10;

FIG. 12 is a cross sectional view taken along the line C-C in FIG. 10;

FIG. 13 is a cross sectional view of a liquid crystal display panel inEmbodiment 2;

FIG. 14 is a perspective view showing the region where a pixel electrodeis formed and a through hole formed in an inorganic passivation film inEmbodiment 2;

FIG. 15 is a perspective view showing a relationship of the drainelectrode, the source electrode, the channel portion, the pixelelectrode and the through hole in Embodiment 2;

FIG. 16 is a plan view of a TFT portion formed in the trapezoidalportion of Embodiment 2;

FIG. 17 is a cross sectional view taken along the line D-D in FIG. 16;

FIG. 18 is a cross sectional view taken along the line E-E in FIG. 16;

FIG. 19 is a cross sectional view taken along the line F-F in FIG. 16;

FIG. 20 is a perspective view of a TFT substrate in Embodiment 3;

FIG. 21 is a cross sectional view taken along the line G-G in FIG. 20;

FIG. 22 is a perspective view of a TFT substrate in Embodiment 4;

FIG. 23 is a cross sectional view taken along the line H-H in FIG. 22;

FIG. 24 is a cross sectional view of a liquid crystal display panel ofEmbodiment 5; and

FIG. 25 is a cross sectional view of a liquid crystal display panel ofEmbodiment 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is to be described in detail in accordance withpreferred embodiments.

Embodiment 1

FIG. 1 is a perspective view for a TFT substrate 100 in a liquid crystaldisplay panel of this embodiment.

FIG. 1 is a perspective view showing a configuration of the TFTsubstrate 100 up to a pixel electrode 106. FIG. 2 is a cross sectionalview of the liquid crystal display panel taken along the line A-A inFIG. 1. FIG. 3 is a cross sectional view along a channel portion 1031 ofa TFT in FIG. 1.

In FIG. 1, a gate line 101 extends in a lateral direction, a drain line104 extends in a longitudinal direction, and a pixel electrode 106 ispresent in a region surrounded by the gate line 101 and the drain line104. The pixel electrode 106 is formed in a solid plane in theconfiguration of FIG. 1. A trapezoidal protrusion is formed below thegate line 101. The trapezoidal protrusion is hereinafter referred to astrapezoidal portion 10. The TFT is formed over the trapezoidal portion10.

In FIG. 1, the drain line 104 is present on the left side of thetrapezoidal portion 10 which serves as a drain electrode 104. Further, asource electrode 105 is formed on the right side of the trapezoidalportion 10. A channel portion 1031 is defined by the space between thedrain electrode 104 and the source electrode 105, and the channelportion 1031 is formed so as to extend on the upper surface and theinclined surfaces of the trapezoidal portion 10.

The pixel electrode 106 is connected directly with the source electrode105 at the inclined surface of the trapezoidal portion 10 not by way ofa through hole. Thus, substantially the whole region surrounded by thegate line 101 and the drain line 104 can be used for forming the pixelelectrode 106. The transmittance of the liquid crystal display panel canbe improved greatly compared with the conventional technology.

FIG. 2 shows a cross sectional view of the liquid crystal display paneltaken along the line A-A in FIG. 1. In FIG. 2, the trapezoidal portion10 is formed on the TFT substrate 100. The gate line 101 is formed overthe surface of the trapezoidal portion 10. A gate insulating film 102 isformed covering the entire TFT substrate 100 including the gate line101. A semiconductor layer 103 of a-Si is formed on part of the gateinsulating film 102. The source electrode 105 is formed over thesemiconductor layer 103.

The pixel electrode 106 and the source electrode 105 are in directcontact with each other on the inclined surface of the trapezoidalportion 10. Thus, a through hole for connecting the source electrode 105of the TFT and the pixel electrode 106 does not exist in thisembodiment. In addition, since the source electrode 105 and the pixelelectrode 106 are connected on the inclined surface of the trapezoidalportion 10, reduction of the transmittance in the connection portiondoes not occur.

An interlayer insulating film 120 is formed covering the sourceelectrode 105 and the pixel electrode 106. A comb-shaped counterelectrode 130 is formed on the interlayer insulating film 120. Thecomb-shaped counter electrode 130 and the pixel electrode 106 (formed ina solid plane in a lower layer) generate lines of electric force betweenthem and rotate liquid crystal molecules to control the lighttransmitting the liquid crystal layer 150 and form an image.

In FIG. 2, a liquid crystal layer 150 is put between the TFT substrate100 and a counter substrate 200. In FIG. 2, an alignment film forperforming initial alignment of liquid crystals is not illustrated. Asshown in FIG. 2, since the TFT and the through hole do not exist in thepixel area in this embodiment, the transmittance of the pixel can beimproved remarkably.

FIG. 3 is a cross sectional view of a channel portion 1031 of the TFTformed over the trapezoidal portion 10. It is necessary to form the TFTon the gate line 101 in this embodiment. However, when the width of thechannel portion 1031 is small, sufficient ON current cannot be obtainedand the switching speed is lowered. As to solve this problem, in thepresent invention, the channel portion 1031 is formed over the uppersurface and the inclined surfaces of the trapezoidal portion 10 tosecure a required channel width.

In FIG. 3, the gate line 101 is formed covering the trapezoidal portion10, and the gate insulating film 102 is formed thereover. Thesemiconductor 103 is formed on the gate insulating film 102 covering theupper surface and the inclined surfaces of the trapezoidal portion 10.Accordingly, substantially the entire surface of the trapezoidal portion10 is used as the channel portion 1031.

When the height H, the top width TW (the length of the upper side), andthe bottom width BW (the length of the bottom side) of the cross sectionof the trapezoidal portion 10 in FIG. 3 are respectively set as H=2 μm,TW=4 μm, and BW=6 μm, the value of T showed in FIG. 3 is 1 μm. When thechannel portion 1031 is formed over the entire trapezoidal surface, thewidth of the channel portion 1031 is; 4+2√5=8.47 μm. When thetrapezoidal portion 10 is not formed, even if the entire part of gateline 101 is used for the channel portion 1031, the width is 6 μm. Thus,the present invention allows the width of the channel portion 1031 to beincreased by 40% or more and the ON current of the TFT can be increasedcorrespondingly.

FIGS. 4 to 9 show a process for forming a main part of the invention.First, as shown in FIG. 4, a trapezoidal portion 10 is formed on a TFTsubstrate 100. The trapezoidal portion 10 is formed at a position wherea gate line 101 is to be formed. Although the gate line 101 is not yetformed at the time the trapezoidal portion 10 is formed, the area of thegate line 101 to be formed is shown by a dotted line in FIG. 4.

The trapezoidal portion 10 can be formed of, for example, aphotosensitive acrylic resin or a phenol resin, etc. The shape of thetrapezoidal portion 10 can be, for example, set as follows; H=2 μm(height), BW×BL=6 μm×10 μm (lower surface), TW×TL=4×8 μm (uppersurface).

FIG. 5 shows a state after the gate line 101 is formed. The width of thegate line 101 is identical with the width of the lower surface of thetrapezoidal portion 10. Thus, the surface of the trapezoidal portion 10is entirely covered by the gate line 101. Then, the gate insulating film102 is formed by SiN sputtering so as to cover the whole area of the TFTsubstrate 100 (not illustrated).

In FIG. 6, a semiconductor layer 103, which is to be the channel portion1031 of the TFT, is formed on the gate insulating film 102. Thesemiconductor layer 103 is formed on the upper surface and the twoinclined surfaces of the trapezoidal portion 10 with a predeterminedwidth. FIG. 7 shows a state after the drain line (electrode) 104 and thesource electrode 105 is formed over the semiconductor layer 103, with aspace between the electrodes for the channel portion 1031. The drainline 104 also serves as the drain electrode of the TFT. As shown in FIG.7, since the channel portion 1031 of the TFT is formed over the uppersurface and the inclined surfaces of the trapezoidal portion 10, thechannel width can be enlarged and the ON current can be increased.

FIG. 8 shows a state after the pixel electrode 106 is formed. The pixelelectrode 106 is formed so that part of the pixel electrode 106 overlapwith part of the source electrode 105 above the inclined surface of thetrapezoidal portion 10 (over which the source electrode 105 is formed).Thus, a through hole for connecting the drain electrode 104 of the TFTand the pixel electrode 106 is not needed in this embodiment.

FIG. 9 shows the drain line 104, the source electrode 105, and the pixelelectrode 106 in hatched lines. The drawing shows that part of the pixelelectrode 106 and part of the source electrode 105 overlap each other onthe inclined surface of the trapezoidal portion 10. As shown in FIG. 9,the TFT and a through hole are not formed in the region surrounded bythe gate line 101 and the drain line 104. Most of the region cantherefore be used for forming the pixel electrode 106, and thetransmittance of the liquid crystal display panel can be improved.

FIG. 10 is a plan view of the TFT formed on the trapezoidal portion 10and a vicinity of the intersection of the gate line 101 and the drainline 104. The drain line 104 and the source electrode 105 are formed onthe left and right side of the trapezoidal portion 10, respectively. Thechannel portion 1031 of the TFT is defined by the space between thedrain line 104 and the source electrode 105. In FIG. 10, part of thepixel electrode 106 extends to the inclined surface of the trapezoidalportion 10 to take electric connection with the source electrode 105.

FIG. 11 is a cross sectional view taken along the line B-B in FIG. 10.In FIG. 11, the gate line 101 is formed covering the surface of thetrapezoidal portion 10, and the gate insulating film 102 is formedcovering the gate line 101. The semiconductor layer 103 is formed abovethe upper surface of the trapezoidal portion 10 (on the gate insulatingfilm 102). The drain line 104 and the source electrode 105 arerespectively formed on the left and right side of the channel portion1031 of the semiconductor layer 103. The channel portion 1031 is definedby the space between the two. Then, an interlayer insulating film 120 ofSiN is formed on the whole area.

FIG. 12 is a cross sectional view taken along the line C-C in FIG. 10.In FIG. 12, the gate line 101 is formed covering the surface of thetrapezoidal portion 10, and the gate insulating film 102 is formedcovering the gate line 101. The semiconductor layer 103 is formed on thegate insulating film 102 covering the upper surface and the inclinedsurfaces of the trapezoidal portion 10. Thus, since the semiconductorlayer 103 is formed over the upper surface and the inclined surfaces ofthe trapezoidal portion 10, the channel portion 1031 of the TFT can beformed with a large width.

In FIG. 12, the source electrode 105 is formed covering thesemiconductor layer 103. The source electrode 105 and the pixelelectrode 106 overlap on one of the inclined surfaces of the trapezoidalportion 10 to take electric conduction with each other. Then, aninterlayer insulating film 120 is formed so as to cover the whole area.In FIG. 2, FIG. 9, FIG. 12, etc., the pixel electrode 106 and the sourceelectrode 105 are in direct contact with each other on the inclinedsurface of the trapezoidal portion 10. In addition, they may also takecontact on the upper surface of the trapezoidal portion 10.

As described above, according to this embodiment, the TFT can be formedover the trapezoidal portion 10 on which the gate line 101 is formed anda through hole for connecting the TFT and the pixel electrode 106 is notneeded. Therefore, the transmittance of the liquid crystal display panelcan be increased without lowering the performance of the TFT comparedwith the conventional structure.

Embodiment 2

FIG. 13 is a drawing of the trapezoidal portion 10 of Embodiment 2,corresponding to a cross section taken along the line A-A in FIG. 1. Inthe drawing, the semiconductor layer 103 is not formed (not shown), anda through hole 110 that does not exist in FIG. 1 (in Embodiment 1) isshown. In Embodiment 1, electric conduction is taken by directlyoverlapping the pixel electrode 106 and the source electrode 105 of theTFT on the inclined surface of the trapezoidal portion 10. However,considering restrictions on a material for the source electrode 105, anetching solution in photolithography, and a material for liquiddeveloper, etc., it may be difficult to adopt the configuration ofEmbodiment 1 in some cases. In such cases, the inorganic passivationfilm 107 is formed on the source electrode 105 and the pixel electrode106 is formed thereon in a solid plane. The interlayer insulating film120 is formed over the pixel electrode 106 and a comb-shaped counterelectrode is formed on the interlayer insulating film 120.

In FIG. 13, the source electrode 105 and the pixel electrode 106 areelectrically conducted by way of the through hole 110. Other operationsin FIG. 13 are identical with those explained in Embodiment 1 referringto FIG. 2.

FIG. 14 shows a part of processes of Embodiment 2. The steps of formingthe gate line 101, the gate insulating film 102, the semiconductor layer103, the drain line 104, and the source electrode 105 over thetrapezoidal portion 10 are identical with that of Embodiment 1. In thisembodiment, an inorganic passivation film 107 of SiN is formedsubsequently. A through hole 110 is formed in the inorganic passivationfilm 107 above the upper surface of the trapezoidal portion 10.

As shown in FIG. 14, a pixel electrode 106 is formed so as to extend tothe upper surface of the trapezoidal portion 10. Thus, the pixelelectrode 106 and the source electrode 105 can be conducted electricallyby way of the through hole 110 formed in the inorganic passivation film107 above the upper surface of the trapezoidal portion 10.

FIG. 15 shows the drain line 104, the source electrode 105, and thepixel electrode 106 in hatched lines. Although the inorganic passivationfilm 107 is formed between the pixel electrode 106 and the sourceelectrode 105, the pixel electrode 106 can be electrically conductedwith the source electrode 105 above the upper surface of the trapezoidalportion 10 by way of the through hole 110.

FIG. 16 is a plan view of the TFT formed over the trapezoidal portion 10and a vicinity of the intersection of the gate line 101 and the drainline 104. The drain line 104 and the source electrode 105 arerespectively formed on the left and right side of the trapezoidalportion 10. The channel portion 1031 of the TFT is defined by the spacebetween the drain line 104 and the source electrode 105. Theseconfigurations are same as that of Embodiment 1. In FIG. 16, the pixelelectrode 106 is formed so that part of the electrode 106 extends to theinclined surface and the upper surface of the trapezoidal portion 10.The pixel electrode 106 is connected with the source electrode 105 byway of the through hole 110 formed in the inorganic passivation film(not illustrated).

FIG. 17 is a cross sectional view taken along the line D-D in FIG. 16.In FIG. 17, the gate line 101 is formed covering the surface of thetrapezoidal portion 10, and the gate insulating film 102 is formedcovering the gate line 101. The semiconductor layer 103 is formed abovethe upper surface of the trapezoidal portion 10 (over the gateinsulating film 102), and the drain line 104 and the source electrode105 are respectively formed on the left and right of the trapezoidalportion 10. The channel portion 1031 of the semiconductor layer 103 isdefined by the space between the drain line 104 and source electrode105. Then, the inorganic passivation film 107 of SiN is formed to coverthe whole area. The through hole 110 is formed in the inorganicpassivation film 10 above the upper surface of the trapezoidal portion10, and the pixel electrode 106 and the source electrode 105 areelectrically connected thereby.

FIG. 18 is a cross sectional view taken along the line E-E in FIG. 16.In FIG. 18, the gate line 101 is formed covering the surface of thetrapezoidal portion 10, and the gate insulating film 102 is formedcovering the gate line 101. The semiconductor layer 103 is formed on thegate insulating film 102, over the upper surface and the inclinedsurfaces of the trapezoidal portion 10. Thus, since the semiconductorlayer 103 is formed covering the upper surface and the inclined surfacesof the trapezoidal portion 10, the channel portion 1031 of the TFT canbe formed with a large width.

In FIG. 18, the source electrode 105 is formed covering thesemiconductor layer 103. The inorganic passivation film 107 is formedcovering the source electrode 105. The pixel electrode 106 is formed onthe inorganic passivation film 107, over the inclined surface and theupper surface of the trapezoidal portion 10. The pixel electrode 106 isin electric conduction with the source electrode 105 in other part (notshown in FIG. 18).

FIG. 19 is a cross sectional view taken along the line F-F in FIG. 16.In the cross section shown in FIG. 19, the semiconductor layer 103 isnot formed and the source electrode 105 is formed on the gate insulatingfilm 102. The inorganic passivation film 107 is formed covering thesource electrode 105, and a through hole 110 is formed in the inorganicpassivation film 107 above the upper surface of the trapezoidal portion10. Part of the pixel electrode 106 extends to the upper surface of thetrapezoidal portion 10, and is in electric conduction with the sourceelectrode 105 via the through hole 110.

The cross sectional structure of the channel portion 1031 of the TFT isidentical with that of Embodiment 1 explained referring to FIG. 3.Similar to Embodiment 1, the TFT is formed over the trapezoidal portion10 on which the gate line 101 is formed, and is not needed to be formedin the pixel area in this embodiment. The transmittance of the liquidcrystal display panel can therefore be improved. In addition, since thethrough hole 110 for electrically connecting the pixel electrode 106 andthe source electrode 105 is formed above the upper surface of thetrapezoidal portion 10 and not formed in the pixel area, the throughhole 110 does not lower the transmittance of the liquid crystal displaypanel.

Embodiment 3

FIG. 20 is a perspective view of the TFT substrate 100 of a thirdembodiment of the invention. In Embodiment 1, the trapezoidal portions10 are formed below the gate line 101. Meanwhile, in this embodiment, acontinuous bank 20 is formed below the gate line 101. Since thecontinuous bank 20 is formed instead of the trapezoidal protrusion, thegate line 101 does not need to be formed on numerous bumps, and the gateline 101 according to this embodiment is less likely to be disconnectedcompared with Embodiment 1.

In FIG. 20, the drain line 104 extends in the longitudinal direction andoverrides the bank 20. The gate line 101 extends in the lateraldirection and covers the continuous bank 20. The pixel electrode 106 isformed in the area surrounded by the drain line 104 and the gate line101. The TFT is formed at the upper surface and the inclined surfaces ofthe bank 20. The drain line 104 also serves as the drain electrode 104over the bank 20, and a source electrode 105 is formed on the right sideof a channel portion 1031 which is defined by the space between them.Since the channel portion 1031 of the TFT is formed at the upper surfaceand the inclined surfaces of the bank 20, the width of the channel canbe enlarged, similarly to Embodiment 1.

In FIG. 20, the pixel electrode 106 extends to the inclined surface ofthe bank 20 and is electrically connected with the source electrode 105in this portion. Thus, the through hole 110 for taking electricconduction between the pixel electrode 106 and the source electrode 105is not necessary in this embodiment as well. FIG. 21 is a crosssectional view taken along the line G-G in FIG. 20. In FIG. 21, the gateline 101 is formed over the bank 20 and the gate insulating film 102 isformed thereover. The semiconductor layer 103 is formed on the gateinsulating film 102, and the drain line (electrode) 104 and the sourceelectrode 105 is respectively formed on the left and right side of thesemiconductor layer 103. The channel portion 1031 is defined by thespace between the drain electrode 104 and the source electrode 105. Theinterlayer insulating film 120 is formed covering the TFT.

Similar to the aforementioned embodiments, the TFT and the thorough hole110 do not need to be formed in the pixel region in this embodiment. Thetransmittance of the liquid crystal display panel can therefore beimproved without lowering the performance of the TFT.

Embodiment 4

FIG. 22 is a perspective view of a TFT substrate 100 according to afourth embodiment of the invention. This embodiment is different fromEmbodiment 2 in that the continuous bank 20 is formed below the gateline 101 instead of the trapezoidal portion 10. Thus, the gate line 101does not need to be formed on numerous bumps. This makes the gate line101 less likely to be disconnected compared with Embodiment 2.

In the configuration shown in FIG. 22, the pixel electrode 106 and thesource electrode 105 are in electric conduction by way of the throughhole 110 formed in the interlayer insulating film 120 above the uppersurface of the bank 20. Except this point, the rest of the configurationshown in FIG. 22 is substantially similar to the configuration shown inFIG. 20 of Embodiment 3. Detailed description of FIG. 22 is thereforeomitted. Similar to the aforementioned embodiments, since the channelportion 1031 of the TFT is formed on the upper surface and the inclinedsurface 20 of the bank 20, the width of the channel can be enlarged.

In FIG. 22, the pixel electrode 106 extends to the upper surface of thebank 20 and is electrically connected with the pixel electrode 105 byway of the through hole 110 formed in the inorganic passivation film107. Thus, the through hole 110 is not formed in the pixel region.

FIG. 23 is a cross sectional view taken along the line H-H in FIG. 22.In FIG. 23, the steps up to the formation of the drain line 104 and theelectrode 105 are identical with the steps described referring to FIG.21 in Embodiment 3. In FIG. 23, the inorganic passivation film 107 isformed over the drain line 104 and the source electrode 105. Both of theinorganic passivation film 107 and the interlayer insulation 120 in FIG.21, which corresponds to the inorganic passivation film 107 in FIG. 23,are formed by SiN sputtering.

The through hole 110 is formed in the inorganic passivation film 107above the upper surface of the bank 20. The source electrode 105 and thepixel electrode 106 extending to the upper surface of the bank 20 iselectrically connected by way of the through hole 110. Then, theinterlayer insulating film 120 (not shown) is formed covering the pixelelectrode 106.

Although the through hole 110 is formed in this embodiment, the throughhole 110 is formed above the upper surface of the bank 20 and does notexist in the pixel region. The transmittance of the pixel region istherefore not lowered. In addition, since the TFT can be formed over thebank 20 without lowering the ON current performance, the transmittanceof the liquid crystal display panel can be improved.

Embodiment 5

The aforementioned embodiments have been explained with reference to theIPS liquid crystal display device. However, in the TN or VA liquidcrystal display device, a problem similar to that of the IPS liquidcrystal display device exists. That is, when the area of the pixel isdecreased, the relative area of the TFT or the through hole 110 isincreased and the transmittance is lowered. Accordingly, the presentinvention described previously is also applicable to the TN or VAsystem.

FIG. 1 is a perspective view of the TFT substrate 100. The configurationof FIG. 1 is applicable to the TFT substrate 100 of the TN or VA systemas well. FIG. 24 is a cross sectional view of part of a TN liquidcrystal display device, the part corresponding to the cross sectionalview taken along the line A-A in FIG. 1. In FIG. 24, the trapezoidalportion 10 is formed on the TFT substrate 100, the gate line 101 isformed covering the trapezoidal portion 10, the gate insulating film 102is formed over the gate line 101, and the semiconductor layer 103 isformed thereon. The source electrode 105 is formed covering thesemiconductor layer 103. The pixel electrode 106 extending from thepixel region and the source electrode 105 are in direct contact andelectrically connected with each other above the inclined surface of thetrapezoidal portion 10.

The inorganic passivation film 107 is formed covering the sourceelectrode 105. The inorganic passivation film 107 is formed so as toprotect the channel portion 1031 formed in other part of the TFT. Acounter electrode 130 is formed to the counter substrate 200, and theliquid crystal layer 150 is put between the counter substrate 200 andthe TFT substrate 100. As described, the same configuration as explainedin Embodiment 1 can be applied to the TFT substrate 100 of the TN liquidcrystal display device, and the transmittance of the pixel area can beimproved. While the above description was made referring to Embodiment1, the bank 20, explained in Embodiment 3, may be applied instead of thetrapezoidal portion 10 in the TN liquid crystal display device as well.

Embodiment 6

FIG. 25 is a drawing of the trapezoidal portion 10 corresponding to thecross sectional view taken along the line A-A in FIG. 1. In the drawing,the semiconductor layer 103 is not formed (not shown) and the throughhole 110 which does not exist in FIG. 1 is formed.

That is, this drawing is a cross sectional view corresponding to FIG. 13in Embodiment 2. In FIG. 25, the gate line 101 is formed over thetrapezoidal portion 10, the gate insulating film 102 is formed over thegate line 101, and the source electrode 105 is formed thereon. Since thesemiconductor layer 103 exist in other part of the trapezoidal portion10 in FIG. 25, the semiconductor layer 103 is not illustrated.

The inorganic passivation film 107 is formed covering the sourceelectrode 105, and the pixel electrode 106 is connected with the sourceelectrode 105 by way of the through hole 110 formed in the inorganicpassivation film 107. The counter electrode 130 is formed to the countersubstrate 200, and the liquid crystal layer 150 is put between thecounter substrate 200 and the TFT substrate 100.

As described, the same configuration as explained in Embodiment 2 can beapplied to the TFT substrate 100 of the TN liquid crystal displaydevice, and the transmittance of the pixel portion can be improved.While the above description was made referring to Embodiment 2, the bank20, explained in Embodiment 4, may be applied instead of the trapezoidalportion 10 in the TN liquid crystal display device as well.

Embodiment 5 and Embodiment 6 have been described by taking the TNsystem for example. The present invention may also be applied to the VAliquid crystal display device in the same manner as described for the TNsystem.

1. A liquid crystal display device comprising: a TFT substrate; gatelines extending in a first direction and arranged in a second directionover the TFT substrate; drain lines extending in the second directionand arranged in the first direction over the TFT substrate; pixelelectrodes each formed in a region surrounded by the gate lines anddrain lines; trapezoidal protrusions formed discretely in the firstdirection below the gate lines, each of the trapezoidal protrusionshaving an upper surface and inclined surfaces in the cross section takenalong a plane orthogonal to the first direction; a gate insulating filmformed over the gate lines; a semiconductor layer formed on the gateinsulating film; drain electrodes formed by the drain lines over thesemiconductor layer; source electrodes formed over the semiconductorlayer; and channel portions defined by the space between the drainelectrodes and the source electrodes, each of the channel portions beingformed covering the upper surface and the inclined surfaces of thetrapezoidal protrusion; wherein the pixel electrode and the sourceelectrode are in contact with each other on the inclined surface of thetrapezoidal protrusion.
 2. A liquid crystal display device according toclaim 1, wherein an interlayer insulating film is formed in a regionsurrounded by the gate line and the drain line, and comb-shaped counterelectrodes are formed on the insulating film.
 3. A liquid crystaldisplay device according to claim 1, further comprising a countersubstrate opposed to the TFT substrate by way of a liquid crystal layerand a counter electrode formed to the counter substrate.
 4. A liquidcrystal display device comprising: a TFT substrate; gate lines extendingin a first direction and arranged in a second direction over the TFTsubstrate; drain lines extending in the second direction and arranged inthe first direction over the TFT substrate; pixel electrodes each formedin a region surrounded by the gate lines and drain lines; trapezoidalprotrusions formed discretely in the first direction below the gatelines, each of the trapezoidal protrusions having an upper surface andinclined surfaces in the cross section taken along a plane orthogonal tothe first direction; a gate insulating film formed over the gate lines;a semiconductor layer formed on the gate insulating film; drainelectrodes formed by the drain lines over the semiconductor layer;source electrodes formed over the semiconductor layer; channel portionsdefined by the space between the drain electrodes and the sourceelectrodes, each of the channel portions being formed covering the uppersurface and the inclined surfaces of the trapezoidal protrusion; and aninorganic passivation film formed over the source electrode; wherein thepixel electrode is formed on the inclined surface and the upper surfaceof the trapezoidal protrusion, and the pixel electrode is connected withthe source electrode by way of a through hole formed in the organicpassivation film above the upper surface of the trapezoidal protrusion.5. A liquid crystal display device according to claim 4, wherein aninterlayer insulating film is formed in a region surrounded by the gateline and the drain line, and comb-shaped counter electrodes are formedon the interlayer insulating film.
 6. A liquid crystal display deviceaccording to claim 4, further comprising a counter substrate opposed tothe TFT substrate by way of a liquid crystal layer and a counterelectrode formed to the counter substrate.
 7. A liquid crystal displaydevice comprising: a TFT substrate; gate lines extending in a firstdirection and arranged in a second direction over the TFT substrate;drain lines extending in the second direction and arranged in the firstdirection over the TFT substrate; pixel electrodes each formed in aregion surrounded by the gate lines and drain lines; banks formedcontinuously in the first direction below the gate lines, each of thebanks having an upper surface and inclined surfaces in the cross sectiontaken along a plane orthogonal to the first direction; a gate insulatingfilm formed over the gate lines; a semiconductor layer formed on thegate insulating film; drain electrodes formed by the drain lines overthe semiconductor layer; source electrodes formed over the semiconductorlayer; and channel portions defined by the space between the drainelectrodes and the source electrodes, each of the channel portions beingformed covering the upper surface and the inclined surfaces of the bank;wherein the pixel electrode and the source electrode are in contact witheach other on the inclined surface of the bank.
 8. A liquid crystaldisplay device comprising: a TFT substrate; gate lines extending in afirst direction and arranged in a second direction over the TFTsubstrate; drain lines extending in the second direction and arranged inthe first direction over the TFT substrate; pixel electrodes each formedin a region surrounded by the gate lines and drain lines; banks formedcontinuously in the first direction below the gate lines, each of thebanks having an upper surface and inclined surfaces in the cross sectiontaken along a plane orthogonal to the first direction; a gate insulatingfilm formed over the gate lines; a semiconductor layer formed on thegate insulating film; drain electrodes formed by the drain lines overthe semiconductor layer; source electrodes formed over the semiconductorlayer; channel portions defined by the space between the drainelectrodes and the source electrodes, each of the channel portions beingformed covering the upper surface and the inclined surfaces of the bank;and an inorganic passivation film formed over the source electrode;wherein the pixel electrode is formed on the inclined surface and theupper surface of the bank, and the pixel electrode is connected with thesource electrode by way of a through hole formed in the organicpassivation film above the upper surface of the bank.